To improve the activity of volcanic rock powder in Hotan area of Xinjiang so as to expand its application to concrete works, this study adopted a commonly used machine grinding method, called the ball-milling method, to refine powder materials and improve their particle distribution. For volcanic rock powders of four sizes, this study investigated the specific surface area with the Blaine method, analyzed the particle grading and distribution with the laser particle size method, verified the change of macro-mechanical properties after the addition of volcanic rock powder with multi-age mortar strength index method, and analyzed the micro morphology and products with SEM and EDS, to reveal the micro change, the macro strength, and the relationship of activity improvement of volcanic ash. The test results show that the machine grinding method can effectively improve the particle distribution of volcanic rock powder, that is to say, the particle size with the passing rate of less than 50% will be reduced by 0. 6-0. 8 μm when the specific surface area is increased by about 80 m²/kg. With the increasing of age, the bending strength and compressive strength of cementitious system added with volcanic rock powder can be continuously improved on a macro level and the increasing rate of bending strength is faster. However, the strength increasing rate is slowed down with fining volcanic rock powder. Through the change of above macro-mechanical properties, the micro observation and analysis with SEM and EDS, the main reason that machine grinding can improve the activity of volcanic rock powder is the filling effects of micro aggregates from refined particles and the improvement of its hydration reaction capacity after addition with the cement-based system.